The present invention relates to a device having a porous surface attached directly or indirectly to a bearing surface and a method for forming the same.
In particular, this invention relates to a computer-aided laser apparatus or other suited high energy beam, which sequentially remelts a plurality of powder layers to build a porous layer in a layer-by-layer fashion.
The present invention also includes a method of attaching or connecting a bearing surface directly or indirectly preferably formed from a polymer to the sequentially-built porous part.
The present application is particularly directed toward a method of forming a porous and partially-porous metallic structure having a bearing surface.
The field of free-form fabrication has seen many important recent advances in the fabrication of articles directly from computer-controlled databases. These advances, many of which are in the field of rapid prototyping of articles such as prototype parts and mold dies, have greatly reduced the time and expense required to fabricate articles, particularly in contrast to conventional machining processes in which a block of material, such as a metal, is machined according to the engineering drawings. One example of a modern rapid prototyping technology is the selective laser sintering process practiced by systems available from 3D Systems, Valencia, Calif. According to this technology, articles are produced in a layer-wise fashion, from a laser-fusible powder that is dispensed one layer at a time. The powder is fused, remelted or sintered, by the application of laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross-section of the article. After fusing of the powder on one particular layer, an additional layer of powder is dispensed, and the process repeated with fusion taking place between the current layer and the previously laid layers, until the article is complete.
The field of rapid prototyping of parts has, in recent years, made large improvements in broadening high strain, high density parts for use in the design and pilot production of many useful articles including metal parts. These advances have permitted the selective laser remelting and sintering process to now also be used in fabricating prototype tooling for injection molding, with expected tool life in excess of 10,000 mold cycles. The technologies have also been applied to the direct fabrication of articles, such as molds from metal powders without a binder. Examples of metal powder reportedly used in such direct fabrication include two-phase metal powders of the copper-tins, copper-solder (the solder being 70% lead and 30% tin), and bronze-nickel systems. The metal articles formed in these ways have been quite dense, for example, having densities of up to 70% to 80% of full density (prior to any infiltration). Prior applications of this technology have strived to increase the density of the metal structure formed by the melting or sintering process. The field of rapid prototyping of parts has focused on providing high strength, high density parts for use and design in production of many useful articles, including metal parts.
But while the field of rapid prototyping has focused on increasing density of such three-dimensional structures, the field has not focused its attention on reducing the density of three-dimensional structures. Consequently, applications where porous and partially-porous metallic structures, and more particularly metal porous structures with interconnective porosity, are advantageous for use, have been largely ignored.
In addition, many structures, especially in the medical arts, require two different surfaces, each adapted for their own purposes. Along this line, a structure may have a first surface which needs to be porous for tissue in-growth and a second surface which should be adapted to be a bearing surface. Further, the first surface or portion may include different layers having different gradients of porosity. For example, the first surface may include an outer region having a porosity of approximately 80%. As you move normal with regard to the first surface the porosity may alter such that the porosity is increased or in a preferred embodiment, the porosity decreases even until the porosity is almost zero. Of course, the present invention contemplates a situation where the porosity alters from position to position depending on the requirements of the device.
Although different techniques have tried to provide such a method and apparatus, still greater techniques are needed in this area.